Metal descaling methods



Sept. 13, 1955 R E CARTER METAL DESCALING METHODS Filed Jan. 9, 1947United States Patent Gti 2,717,845 METAL DESCALING METHODS Roy E.Carter, Warren, Ohio Application January 9, 1947, Serial N o. 721,041 4Claims. (Cl. 134-2) The invention relates to methods for the descalingof metal by subjecting the metal having scale or oxides on its surfacesto a molten bath which removes oxygen from an ashy substance that may bereadily removed or washed off.

Such descaling has been accomplished in a batch type operation bysubjecting a metal piece having oxide coatings on its surfaces to amolten salt bath including sodium hydride. Metal descaling processes bythe use of sodium hydride in batch type ried out for example by twoprior processes.

In the case of one process, a sodium hydroxide bath is maintained at atemperature of 700-750 F. and metallic sodium and hydrogen are added tobuild up in the bath a sodium hydride content of 1.5% to 2%.

ln the other process the salt bath contains all the necessary elementswithout additions, and includes sodium hydroxide, and the bath isoperated at a temperature of 900 F.

The batch type operations used heretofore in both of these sodiumhydride metal descaling processes in which metal are separately subjectto the action of the in 1946, particularly stainless steel sheets andstrips.

As above indicated, the molten salt baths of both the prior sodiumhydride descaling processes include sodium hydroxide. ln each case thebath is maintained molten by externally applied heat.

even under controlled prices and greater detail in Fig. 2, and

Molten sodium hydroxide baths have long been used for treating metals invarious specific manners, in many instances the bath being electrolyzed,and in some instances the article being treated being a part of theelectrolytic circuit.

By using an externally heated molten salt bath as in two priorprocesses, ment is eliminated.

The nature of the present invention may be stated general terms asincluding methods including succesthe necessity for electricalequipsive` sequential steps, by which a continuous strip of moving metaland particularly stainless steel may be subindicated generally by 16.

2,717,845 Patented Sept. 13, 1955 ject generally to a molten bathtreatment which is adequate at a speed of 30 to 100 feet per minute ormore of the strip, and particularly to a molten descaling bathtreatment, the bath preferably containing sodium hydride.

As compared with an acid bath, in a molten descaling bath hydroxide, thesodium hydride acts on oxides only, whereas an acid bath attacks bothoxides and the parent metal.

By way of example, embodiments of apparatus for carrying out the methodof the present invention, thereof, are illustrated in the accompanyingdrawing forming a part hereof, and in which Figure l is a diagrammaticView, partly in Vertical elevation, and partly in vertical sectionshowing one form methods hereof;

Fig. 2 is an enlarged transverse sectional View thereof as on line 2 2,Fig. 1, with details added and distant parts removed; and

Fig. 3 is another enlarged transverse sectional View thereof as on line3-3, Fig. l, with details added and distant parts removed.

Similar numerals refer to similar parts throughout the drawing.

The apparatus for metal treatment, and particularly for metal descaling,is indicated generally by 1t) in Fig. l, and the apparatus 10 as shownis part of a continuous annealing, descaling, and pickling line for anelongated metal piece 11 as shown a metal strip, and particularly astainless steel strip. The elongated metal strip 11 is movedlongitudinally means. indicated generally by 14, second radiant heatingmeans indicated usual construcand withln its compartment the strip 11 issubject annealing furnace 12 has an ex1t opening 18 from which the strip11 emerges and into the entrance opening 20 heating means 13.

The first radiant heating refractory material 26. The rectangular tubeof the first radiant heating means 13 formed by the walls heatingelements 28 are located, each heating element 28 extending between andhaving its ends supported in, as shown, the rst radiant heater sidewalls 22a and 22b.

Similarly, below the strip 11 in the passageway 27 of the first radiantheating means 13, another set of radiant heating element 28 is located.Each of the radiant heating elements 28 may be a tube of radiant heatresistant metal alloy which is heated to radiant heat by an internalflame, or when desired each of the radiant heating elements 28 may be anelectric resistance radiant heating element which is maintained atradiant heat by being located in series with a source of electric power.Such an internally llame heated tubular radiant heating element, or suchan electric resistance radiant heating element, is of usual constructionand operation, and any other desired form of radiant heating element maybe utilized, such as a metal member brought to radiant tcmperature byelectric induction heating.

The first radiant heating means 13 has an exit opening 29 from which thestrip 11 emerges, preferably passing over a level and guide roller 30above the entrance end 31 of the immersing bath means 14.

The immersing bath means 14 includes an elongated upwardly opening tankindicated generally by 32 and having an upwardly opening elongatedcompartment 33 extending from the entrance end 31 to the exit end 34. Alevel and guide roll 35 extends laterally in the compartment 33 betweenside walls of the tank 32 at the entrance end 31, and the roll 35 islongitudinally spaced from and below the level and guide roller 30.Similarly within the compartment 33 of the tank 32 at the exit end 34, alevel and guide roll 36 extends between said walls of the tank, andlongitudinally spaced from the roll 36 and above the exit end 34 of theimmersing bath means, there is located a level, guide, and heater roll37.

The strip 11 extends downwardly from the roll 3) into the entrance end31 of the compartment 33 of the tank or container 32 of the immersingbath means 14. The Strip 11 then extends under the roll 35 andlongitudinally through the compartment 33 to and under the roll 36 andupwardly therefrom to and over the roll 37 The tank 33 is filled withthe desired liquid metal treating material to a level above the portionof the strip 11 extending between the rolls 35 and 36.

The immersing bath means 14 may have details of construction shown inFig. 3 in which inner walls of the tank 32 are steel walls indicatedgenerally by 38 resting in a trough formed in outer refractory wallsindicated generally by 39. The tank steel walls 38 as shown include sidewalls 49a and 40h, and the tank outer refractory walls include sidewalls 41a and 41h alongside the tank steel walls 46a and 40]), and therefractory side walls 41a and 41h having longitudinally extending sideopening channels 42a and 42h formed therein, the channels openingtowards the steel side walls 40a and 4Gb.

Longitudinally extending baffle means 43a and 43b are located in thechannels 42a and 42h, and each side wall 41a and 41b has a plurality ofinwardly flaring burner openings 44 formed therein at the outer smallerend of each of which is located the tip end of a gas burner nozzle 45,the flame from which in operation impinges the opposite baffle wall 43aor 43b, whereby the tank inner steel walls 38 are heated to the desiredtemperature for transmission to the liquid or molten material in thecompartment 33 of the tank or container 32.

The second radiant heating means is interposed between the rolls 36 and37, and is of a construction generally similar to the first radiantheating means 13, with suitable dimensional changes. In the secondradiant heating means 15, the strip 11 passes into a lower entrance endopening 46-1 and upwardly through the passageway 46-2 of the secondradiant heating means 15 and out the exit end opening 46-3 thereof andover the roll 37.

The liquid spray means 16 includes upper walls forming a tunnel 48having an entrance end opening 49 and an exit end opening 50. The bottomof the tunnel 48 opens into an upwardly opening drain pit 50-1.Intermediate the ends of the tunnel 48 and between the side wallsthereof, a level and guide roll 52 extends. The guide roll 37 isadjacent and outside of the tunnel entrance end opening 49, and adjacentand outside of the exit end opening 50 of the tunnel 4S, a level andguide roll 51 is located. The strip 11 passes into the tunnel from theroll 37 downwardly beneath the roll 52 and upwardly over the roll 51from which it passes into the usual pickling tank 17. Above the strip 11within the tunnel passage 53 there is located one set of liquid spraynozzles each indicated by 54, the spray 55 of each of which is directeddownwardly onto the top surface of the strip 11. Below the strip 11 inthe tunnel passageway 53, another set of liquid spray nozzles eachindicated by 54 each directs its spray 55 upwardly against the bottomsurface of the strip 11.

The operation of the improved apparatus 10 for carrying out the improvedmethods hereof, preferably for pickling a stainless steel strip 11, isas follows: The cornpartment 33 of the tank or container 32 of theimmersion bath means 14 is filled with a bath 56 of desired metaltreating material which may be either liquid or molten, but for thepurposes of descaling stainless steel may preferably be a molten sodiumhydroxide bath containing metallic sodium and hydrogen as in the iirstabove described batch sodium hydride descaling process. The bath 56 hasits upper surface 57 at a level substantially above the portion of thestrip 11 extending between the rolls 35 and 36, and the temperature ofthe bath 56 is maintained at the desired temperature of 70D-750 F. inthe first above described batch process, by operation of the gas burners45. The interior temperature of the compartment of the annealing furnace12 containing one or more gases is maintained at a usual annealingternperature. The temperature within the passageway 27 of the firstradiant heating means 13 is maintained preferably at least equal to andpreferably above the temperature of the bath 56 of molten material.Likewise, the temperature in the passageway 46-2 of the second radiantheating means 15 is maintained at a temperature at least equal to orabove the temperature of the bath 56 of molten material.

The heating capacity of the first radiant heating means 13 is sufficientto bring up and maintain the temperature of the portions of the strip ormetal piece 11 passing therethrough somewhat above the temperature ofthe bath of molten material 56, so that none of the heat of the bath 56is required to heat the metal strip or piece 11 as it passestherethrough. The temperature of the strip 11 as it passes through thesecond radiant heating means 15 is likewise maintained above thetemperature of the bath 56 of molten material so that the adhering saltmixture on the metal strip 11 is maintained uid preventing solidcationof the salt on the strip 11 which otherwise would cause marks orscratches on the iinished or partly finished surfaces of the strip 11,and which also would result in excessive carry out of the salts of thebath 56.

The tunnel or box 48 of the liquid spray means 16 is provided withsuitable shielding means at its entrance end opening 49 and at its exitend opening 50. Each spray nozzle 54 is served with water at arelatively high pressure of upwards of 500 pounds per square inch, andthe high pressure liquid spray means 16 serves to thoroughly removeadhering salt and descaling residue from the surfaces of the strip 11.Adhering salt otherwise would reduce the acid concentration in thepickling tank 17, usually containing nitric acid.

The level guide and heater roll 37 is maintained by internal heatingmeans at a temperature of upwards of 700 F. or more to further maintainthe temperature of the strip 11 as it passes out of the second radiantheating means 15.

The strip 11 is passed in sequence through the annealing furnace 12, thefirst radiant heating means 13, the immersing bath means 14, the secondradiant heating means 15, means 16, and the pickling tank 17, andsubsequent subpparatuses by usual means such as tension rolls located atthe right of the parts illustrated in Fig. 1.

By reason of the improved relation of the steps of the improved methodshereof and the apparatus parts for carrying out the improved methodsteps, satisfactory descaling may be attained when using the sodiumhydroXide and sodium hydride descaling molten material in the bath 56 ata speed of the moving metal strip or piece 11 of 30 to 100 feet perminute.

In the treatment of the elongated metal piece 11 by operation of theimproved apparatus to carry out the treatment of the elongated bedescribed as including method steps including moving the elongated metalpiece 11 longitudinally in one direction (from left to right in Fig. l)and successively subjecting portions of the metal piece 11 to aplurality of diiierent actions in sequence, each action taking place inone of the component subapparatuses or metal treating means 12, 13, 14,15, and 16, as above described.

The embodiments of the present improvements illustrated and describedherein are by way of example, and the scope of the present invention isnot limited to the same or to the particular details thereof but iscornmensurate with any and all subject matter contained herein which mayat any time properly under the U. S. patent laws be set forth in theclaims hereof or originating herein, and the elements of any such claimsare intended to include their reasonable functional and structuralequivalents.

I claim:

1. In the treatment of an elongated metal piece, the method stepsincluding moving the elongated metal piece longitudinally in onedirection and ing successive portions of the metal of different actionsin sequence, as contact with one or more hot gases, a first heatingsubsequent to the gas heating, immersion in a bath of nor:- aciddescaling liquid material consisting of molten sodium hydroxide andmolten sodium hydride, a second heating piece to a plurality follows:heating by successively subjectand impingement by water mersion, andimpingement by water sprays.

3. In the treatment of metal, the method steps including maintaining ahot liquid temperature.

4. In the treatment of an elongated metal piece, the method stepsincluding moving the elongated metal piece longitudinally in onedirection and successively subjecting successive portions of the metalpiece to a plurality of different actions in sequence, as follows:heating by contact with one or more hot gases, a iirst heatingsubsequent to the gas heating, immersion in a bath of nonacid descalingliquid material consisting of molten sodium hydroxide and molten sodiumhydride, a second heating subsequent to the immersion, and impingernentby water sprays, the pressure of the liquid sprays being upwards of 500pounds per square inc References Cited inthe le of this patent UNTEDSTATES PATENTS

1. IN THE TREATMENT OF AN ELONGATED METAL PIECE METHOD STEPS INCLUDINGMOVING THE ELONGATED METAL PIECE LONGITUDINALLY IN ONE DIRECTION ANDSUCCESSIVELY SUBJECTING SUCCESSIVE PORTIONS OF THE METAL PIECE TO APLURALITY OF DIFFERENT ACTIONS IN SEQUENCE, AS FOLLOWS; HEATING BYCONTACT WITH ONE OR MORE HOT GASES, A FIRST HEATING SUBSEQUENT TO THEGAS HEATING, IMMERSION IN A BATH OF NONACID DESCALING LIQUID MATERIALCONSISTING OF MOLTEN SODIUM HYDROXIDE AND MOLTEN SODIUM HYDRIDE, ASECOND HEATING SUBSEQUENT TO THE IMMERSION, AND IMPINGEMENT BY WATERSPRAYS.